There is a requirement in many rotating systems to be able to transfer fluid under pressure across an interface where there is relative rotation between two parts of the system.
A conventional solution to this requirement involves the use of sliding seals which are then subjected to the difference between the local ambient pressure and the pressure of the fluid being transferred.
A known disadvantage of the use of sliding seals is the potential for seal leakage with the consequent leakage and loss of the transferred fluid. This in turn can have a deleterious effect on components fed by the transferred fluid, such as damage to gears and bearings caused by a loss of lubricant.
In aerospace gas turbine applications, this may cause in-flight engine shutdown, aircraft diversion and/or unplanned engine removal.
An alternative conventional solution to the above-mentioned fluid transfer requirement is the use of a scoop that uses the relative rotation to collect oil from a trough using the dynamic pressure head resulting from the difference in rotation.
A disadvantage of the dynamic scoop approach is that the dynamic pressure head is dependent upon the rate of rotation of the fluid receiving system. In situations where this rate of rotation is low, such as the planet carrier of an epicyclic gearbox, the pressure that may be developed may be insufficient to supply an oil jet or hydraulic actuator with the necessary fluid pressure.
As outlined above, a common aerospace application requiring fluid transfer between rotating components is the planetary epicyclic gearbox used in a gas turbine engine. In one such application, a gearbox input may be connected to the sun gear and rotating at high speed, with a gearbox output being connected to the planet gear carrier and rotating at low speed. It is desirable to be able to supply pressurised oil to the planet bearings.